1. Field of the Invention
The present invention relates to a method and device for monitoring a station of a landing aid system of the MLS (Microwave Landing System) type, whose transmission circuits are doubled.
2. Description of the Prior Art
Systems for aid to air navigation, and more particularly landing systems, must offer a maximum of safety, because of their function. The structure of these systems comprises then the following functional assemblies:
an assembly of circuits transmitting the guidance signals;
an antenna;
a monitoring device.
The purpose of the monitoring device is to check the conformity of the parameters of the guidance signal transmitted with the standards laid down by the ICAO (International Civial Aviation Organization). In the case of too wide a discrepancy, the monitoring device must stop transmission.
It is known, more particularly for landing aid systems of the ILS (Instrument Landing System) type to double the transmitting assembly so as to increase the availability of the whole of the system. Such a configuration is shown in FIG. 1.
In this FIG. 1, the two separate transmission assemblies are referenced 1 and 2. They may be connected, one or the other, to an antenna 5 through a switching device 3. The other transmitting assembly is then connected to a load 4. The system further comprises two monitoring assembles. The first, referenced 7, is charged with monitoring the transmission assembly in service, that is to say the one which is connected to antenna 5 at a given moment. The assembly 7 may include for example a device for monitoring the transmission assembly in service before the antenna (connection 71). Such a device is often called internal monitor. The assembly 7 may further include a device for monitoring the transmission assembly in service together with the antenna (connection 72). This latter device is often called external monitor. The second assembly 6 is charged with monitoring the stand-by transmission assembly namely the one which is connected to load 4.
Operation of the two transmission assemblies 1 and 2 is permanently monitored by the two assemblies 6 and 7. When, for example, the transmission assembly in service has a defect, its monitoring assembly (7) through a control logic device not shown in FIG. 1 causes switching (3) to antenna 5 of the other transmission assembly, which was previously standing by. The transmission assembly previously in service is then switched to the load, or stopped completely, depending on the seriousness of the defect discovered.
It is apparent that such a structure uses two monitoring assemblies (6 and 7).
This structure is widely used for the ILSs. It can also be used for a system of the MLS type. However, this latter has the characteristic, with respect to the ILS, of being designed about an electronic sweep (or scanning) antenna. The preceding monitoring system has then the drawback of not allowing checking of the overall operation of the stand-by transmission assembly in association with this antenna, which is a serious drawback because of the relative sophistication and fragility of such an antenna.
An object of the present invention is to provide a method and device which are adapted to the MLS, that is to say which monitor all the components thereof, including the electronic sweep antenna and this under operating conditions.